The invention relates to a method for the connection of pieces of textile fabric. More particularly, the invention relates to a method for the production of a textile band and a textile band thus produced.
Textile materials are used in large quantities in the production of a multiplicity of products. As an example, the production of a mattress may be mentioned here, in which a band is fed mechanically and is stitched to the mattress all round the latter.
For the mechanical processing of textiles of this type, continuously produced textiles, for example bands, are required. These are, for example, applied to suitable carriers, for example wound on rolls, or introduced loosely in containers. However, in the continuous production of textiles by means of known production methods, for example weaving, braiding, double ribbing, knitting, the formation of defects cannot be entirely ruled out. Defects of this kind may be discovered during a subsequent check. However, there is no possibility of removing such defects other than cutting the textile product. This yields continuous textile products of varying length.
This, in turn, presents serious difficulties in the continuous processing of such a continuous textile product. If a delivered unit contains a plurality of portions of irregular length, the respective lengths have to be taken into account during processing. For example, for processing a band by sewing on a mattress, a band has to be fed in one piece, so that it is always necessary to check whether there is still sufficient band length. This leads to a very high outlay.
It is thus desirable to provide a method of reconnecting the ends of a textile product after cutting out the defective part.
A known method of connection for textiles which have a certain proportion of synthetic fibres is welding with the aid of ultrasound. EP-A-001581 describes such a method for the connection of textiles which have a proportion of at least 50% of thermoplastic fibres or threads. Two textile pieces are pressed together between a sonotrode and an anvil and vibrations are generated in the ultrasonic range. A number of welds which are arranged in two rows are produced by small tips. The document recommends that paper be interposed in order to distribute the pressure more effectively and achieve greater strength.
DE-A-42 33 878 shows a device for the welding and separation of edging bands in the production of blankets. The upper and lower parts of a band stitched longitudinally to a blanket are welded ultrasonically between an upper and a lower die with the aid of two seams arranged at a distance from one another. The band is separated between the seams thus formed. Plane surfaces are used for welding.
CH-A-615965 presents an ultrasonic sewing machine for the welding of textile material. A ram provided with a welding pattern or with a cutting edge presses the weldable material against a sonotrode capable of being set in vibration ultrasonically.
DE-A-195 32 499 shows a device for ultrasonic cutting, in which an ultrasonic head with a sonotrode and with a working blade, when pressed against a round stay, vibrates at ultrasonic frequency and thus cuts up textile broad-fabric webs. It is indicated that the device may also be used for ultrasonic welding
The connection methods known so far achieve the task of connecting pieces of textile fabric. However, the known connections have proven to create problems if the connected products are to be further processed automatically.
The object of the invention is to specify a textile band or continuous textile product and a method for producing it, a textile product suitable for continuous automatical processing being provided in a simple and cost-effective way.
It has not been possible hitherto to reconnect the continuous textile products, in particular bands, cut apart for the removal of defects, in such a way that it has been possible to process them in the same way as fault-free textile products. This is because the corresponding connections must be such that, for example, a band can continue to be processed mechanically, that is to say guided by corresponding feeds. For this purpose, the connections must have, on the one hand, the necessary strength, but, on the other hand, also some elasticity. Moreover, the processability of the band, that is to say, in particular, further stitching, must also be possible even at a connection point.
In the connection method according to the invention, two textile pieces are laid one on the other, with an overlap, between a sonotrode and an anvil and are welded to one another ultrasonically. For this purpose, with the aid of suitable devices known to a person skilled in the art, the sonotrode is set in vibrations, the frequency of which is in the ultrasonic range. The textile pieces clamped between the sonotrode and the anvil functioning as a fixed counterpiece are thereby set in rapid movement, so that the thermoplastic fibres fuse or are plasticized and are connected to one another. This results in a connection of the textile pieces which is uniform over the entire surface.
The invention is based, in this case, on the knowledge that previous methods for the ultrasonic welding of textile pieces either did not offer sufficient strength or did not have sufficient processing properties. This problem is solved, according to the invention, in that the textile pieces are xe2x80x9ccut off hotxe2x80x9d at the margins of the regions to be connected to one another, that is to say a cut edge is formed such that the threads of the textile fabrics are essentially bound at the edge. It is known to a person skilled in the art that such an effect occurs, for example, as a result of ultrasonic cutting, but can also be achieved by other measures. It is critical that at least large proportions of the threads are bound at the edge, for example by plasticization.
The aim, here, is to form a weld seam at which plasticization of the synthetic fibres contained in the fabric takes place only at particular points, distributed as effectively as possible over the welding region. It has been shown that, in the case of high pressure and a long welding operation, large regions are plasticized, which may be undesirable with regard to the processing properties. In particular, these connections also become brittle, that is to say the textile character is lost.
According to the invention, the surfaces of the anvil and/or sonotrode are not smooth, but have a surface profile. By this is meant a pattern of elevations and depressions. By means of such a profile, the pressure is distributed in a suitable way and the material flow is influenced. As already mentioned, the aim is to maintain the textile character even at the weld. This is achieved by means of a number of locations, distributed over this region, at which plasticization occurs and individual threads are connected. It is preferred that these locations do not merge into one another, but that, between the plasticization locations, there are in each case still portions in which the fabric is still textile, that is to say is not plasticized. The plasticization locations should, as far as possible, be on the inside where the pieces to be connected lie one on the other.
A particularly preferred surface profile is a cross-grooved profile, in which pyramidal elevations arranged in rows and columns are applied closely next to one another on the surface of the anvil. The tips in this case define the locations at which plasticization first occurs.
In a preferred refinement, the two dies, between which the textile pieces are pressed together during processing, that is to say the anvil and sonotrode, have surface profiles. It is preferred, in this case, that surface profiles fitting one into the other be used, that is to say that elevations of one die are located opposite depressions of the other die. For this, because of the clearance which remains in any case, even approximate interengagement is sufficient; the profiles do not have to engage one into the other entirely without a gap.
Both the surface profile and the further method parameters (ultrasonic frequency amplitude, pressure, duration, etc.) should be selected according to the types of fabric to be processed in each case. For example, for very fine fabrics a markedly shorter welding duration, along with markedly lower welding energy, is necessary than for very coarse fabrics. The surface profile should in this case preferably be selected according to the structure of the processed textile fabric. Accordingly, for example, a correspondingly coarse grooving may be selected for coarse fabrics, whilst fine fabrics also require a finer structure of the surface profile.
The connection of the textile pieces is to take place in such a way that the textile character is preserved. This is the case when full-area plasticization does not occur but, instead, merely a fusion of threads of the two textile pieces which takes place at particular points.
The cut edges thus formed may have any desired shapes. Straight edges running transversely to the feed direction are simple. For automatic processing and threading into feeds, it may also be advantageous to have a connection in which the weld seam runs obliquely. Cut edges running correspondingly obliquely are then also preferably formed. In principle, any runs of the weld seam and of the cut edges may be considered, including also curved runs and sinuous shapes.
By two textile pieces, in which the cut edges have previously been formed in this way, being laid one above the other and connected, surprisingly high strength can be achieved even on small overlap regions. Above all, in this case, it is possible to connect the bands permanently, without supplying welding energy for too long. Thus, excessive fusion of the bands is avoided, so that, even at the connection point, the textile character of the bands is preserved and these continue to remain easily processable, that is to say can be pierced for stitching and can also be threaded through mechanical feeds.
When pieces of bands are joined to one another, it is preferred that they be laid one on the other with cut edges pointing away from one another and be welded in the overlap region. A particularly thin seam can thus be formed. The selected width of the overlap region may differ greatly, depending on the application and on the band used. Overlap regions of 0.2 to 2 cm are preferred. A strip having a width of approximately 0.7 cm is particularly preferred as an overlap region. Moreover, at the same time, it is preferred that as large a part of the overlap region as possible also be part of the welded connection. This should be at least 50% of the overlap region, preferably at least 80%, particularly preferably even the entire overlap region. During the welding of two bands of identical width, it is preferred that welding be carried out over the entire width of the bands.
In the method for the production of textile bands the textile bands are first produced continuously and weaving faults which occur are cut out. The cuts are connected to one another by means of the ultrasonic welding method, as already explained above. Thus, bands to be processed continuously can be produced and can be applied to a suitable earlier, for example a roller, or be introduced for further processing into a container. Since the method parameters are selected, depending on material, in such a way that, for example, a band continues to be processable automatically, such carriers can be used in feed devices for the automatic stitching of the band and be fed and processed continuously.